Multi-stage processes are commonly implemented in the manufacture of mechanical and electrical components such as gears, cams, pistons, rods, bolts, springs, fittings, circuit boards, capacitors, inductors, receivers, etc. For example, the process of manufacturing a gear from a gear blank may require the blank to pass through a drilling or boring stage where a central hole is rough bored through the flat face of the blank. The blank then passes through a stage where teeth are hobbed or otherwise formed along the outer radial perimeter of the blank. Some types of gears have hubs with threads. The gears are heat treated for hardness, and the threaded ends are annealed to relieve the stresses and brittleness caused by the heat treatment. The teeth and central hole are then precision ground so that the center of the pitch radius of the teeth coincides with the center of its hole.
Each manufacturing step or stage is performed by a separate machine or tool. For example, during a gear manufacturing operation, a gear blank is brought to a first station and loaded onto a first machine that performs a first task on the blank. The gear is then unloaded from the first machine, transported to a second station, and loaded on a second machine where another task is performed, and so on. This loading, machining, unloading and transporting process continues until each required task is complete.
One problem with multi-stage manufacturing operations is that they are often time consuming, labor intensive, and dangerous for the workers. The workers must walk by the machines when carrying heavy loads of workpiece, and load those parts into or onto the machines. Some machines contain fast moving and rotating parts. Other machines involve extremely hot temperatures or caustic acid baths. Hot shrapnel and caustic fluid is often thrown from the machines as the parts are drilled, sawed, ground, polished, and sprayed. Although shields are typically provided, they may not prevent all discharges, particularly if the shield is inadvertently left open. A worker that stands or walks in the wrong area, fails to put on proper safety attire, or accidentally slips, falls or leans against a machine can be severely hurt. Yet, safety precautions are inconvenient and frequently come at the expense of productivity. Workers may cut comers to meet or exceed desired productivity levels.
To speed up the manufacturing process and reduce labor requirements, stand-alone machines have been designed to hold a number of workpieces, and consecutively perform a single manufacturing process on those workpieces. For example, U.S. Pat. Nos. 2,329,301 and 3,728,829 disclose stand-alone, gear manufacturing machines that hold and dispense blanks through chutes to a position where a grinding or honing operation is performed to form the central bore of the gear. U.S. Pat. Nos. 3,533,258 and 4,106,632 disclose stand-alone machines that load gear blanks via chutes, and loading mechanisms that position the blanks into positions where a rolling operation is performed to form the teeth. In addition, U.S. Pat. No. 3,541,921 discloses an indexible, stand-alone, beveled gear cutting machine and control system that includes a three-armed turret. The turret picks up a gear piece from a first supply station, rotationally moves the piece to a first sequential station where a first finishing operation is performed, then move the piece to a second sequential station where a second finishing operation is performed, and finally return the gear piece to the supply station.
FIGS. 1-3 show a conventional gear grinding operation for gear pieces 5 having relatively flat side faces 6, a generally circular outer surface or perimeter 7 with uniformly spaced, precision cut teeth 7a, and an inner surface 9 that forms a rough cut central opening 9a. The gear pieces 5 are ground via a grinding machine 10 with a continuously rotating chuck 12 of the type shown in FIG. 4. The chuck 12 has three jaws or brackets 13. Each jaw 13 has a dog 14 and a locator tooth 16. As the dog 14 attempts to enter between the teeth 7a of the gear piece 5, it imparts rotation to the gear piece and syncronizes that rotation with the chuck 12 as shown in FIG. 5. Once the dog 14 has entered between two teeth 7a, the locator tooth 16 enters between two other teeth 7a. The jaws 13 then extend the locator teeth 16 to firmly grip the gear piece 5 as shown in FIG. 6. Once gripped, the locator teeth 16 align the gear piece 5 so that the central axis of the pitch diameter of the gear teeth 7a are aligned with the central axis of the grinding tool. Conveyors 20 and 21 supply gear pieces 5 to and discharge them from this manufacturing operation.
The grinding machine 10 is combined with a conventional, stand-alone, loading/unloading machine 30. The loading/unloading machine 30 has a frame 31 that supports a relatively large hydraulic or pneumatic expansion cylinder 32. The cylinder 32 supports a bar 33 formed in the shape of a boomerang with an angle of about 120xc2x0. Each end of the bar 33 has a gripping arm 35 for gripping one gear piece 5. One end of each gripping arm 35 is rigidly fixed to the bar 33. The other end of the gripping arm 35 has a sleeve 36 that is free to rotate about its central axis. The central expansion cylinder 32 drives the bar 33 and both gripping arms 35 toward and away from the grinding machine 10. The expansion cylinder 32, rotatable bar 33 and two gripping arms 35 form a loader/unloader unit 39.
A balloon-type gripping device 37 is situated around the outside of the rotatable sleeve 36 of each gripping arm 35 as shown in FIG. 3. The fixed end of the bar 33 has a pneumatic or hydraulic line that controls the balloon-type gripping device 36. The machine 30 inflates the balloon-type gripping device 36 to grip the inside surface of the central opening 9a of a gear piece 5, and deflates the device to let go of the gear piece. In an alternate embodiment, the balloon-type gripping device 37 is replaced with a locking ball and a plunger device.
As best shown in FIG. 1, the machine 30 rotates the bar 33 gripping arms 35 of the loader/unloader unit 39 in a clockwise or counterclockwise direction about the central axis of the expansion cylinder 32. The bar 33 rotates through a cycle in which each gripping arm 35 travels to a pick-up position, a load/unload position, and a discharge position. In the pickup position, one gripping arm 35 is aligned with a gear piece 5 on the supply conveyor 20. In the load/unload position, one gripping arm 35 is aligned with the rotating chuck 12 of the grinding machining 10. In the discharge position, one gripping arm 35 is aligned with the discharge conveyor 21.
During operation, the expansion cylinder 32 is used to horizontally extend and retract the bar 33 and gripping arms 35 at each of the pick-up, load/unload, and discharge positions. To pick-up a gear piece 5, one arm 35 of the gripping device 37 enters the central hole 9a of the gear piece 5 on the supply conveyor 20 and its balloon is inflated to grip that gear piece. The cylinder 32 is then retracted to pull the gripping arm 35 and gear piece away from the supply conveyor 20. To load a gear piece 5 onto the rotating chuck 12, the bar 33 rotates the gripping arm 35 and gear piece 5 into alignment with the rotating chuck 12. The expansion cylinder 32 then extends the rotatable sleeve 36, gripping device 37 and non-rotating gear piece 5 toward the chuck 12. The dog 14 of the chuck enters between the teeth 7 of the gear 5 to impart rotational movement to the gear, and the locator teeth 16 then enter between the teeth 7a. After the locator teeth 16 firmly grip the gear piece 5, the balloon is deflated to release that gear piece, and the cylinder 32 is retracted to pull the gripping arm 35 away from the chuck 12. To unload a gear piece 5 from the rotating chuck 12, the bar 33 rotates the empty gripping arm 35 into alignment with the rotating chuck 12 and gear piece 5. The expansion cylinder 32 then extends the rotatable sleeve 36 and gripping device 37 into the central hole 9a of the gear piece 5. The balloon type gripping device 37 is inflated to grip the gear piece 5, and the cylinder 32 is retracted to pull the gripping arm 35 and gear piece away from the chuck 12.
One problem with conventional stand-alone workpiece manufacturing machines is that each machine requires its own loading/unloading unit and supply and discharge conveyors. These loading/unloading units and conveyors are expensive, bulky and require a great deal of floor space. Each loading/unloading unit and conveyor also requires its own maintenance schedule. Should any part in the unit or conveyor jam or fail, the machine and the entire manufacturing operation may be shut down. Each time a worker goes near one of the loading/unloading units, the manufacturing operation must be shut down or the worker is exposed to possible injury.
Another problem with conventional, stand alone machines is that it is difficult to change over an assembly line using several machines to form a particular part. Each machine has to be set up to handle a workpiece of a particular size and shape. For example, in order to produce gears having a three-inch diameter, twenty-two teeth with a given pitch diameter and a one-inch diameter central hole, each stand-alone machine has to be adjusted to perform its specific task for this specific part. Then, the first machine in the assembly line must be loaded with specific gear blanks and processed. A substantial lag time can occur before the second and third machines in the process are ready to be filled with workpieces. In addition, many hours can be required to set up and test the accuracy of the machines. Manufacturing operations of this type are not conducive to small part runs, which are frequently required in the just-in-time manufacturing operations in use today.
A further problem associated with conventional, stand-alone, and indexible machines is that some manufacturing operations take longer than others. Indexible machines can only be incremented as quickly as it takes to complete the slowest machining operation. While only a few seconds may be needed to rough bore a hole in a gear piece, several minutes may be required to anneal that gear piece.
A still further problem with conventional stand-alone and indexible machines is that they do not incorporate gripping devices appropriate for a robotic application. Conventional machines impart specific types of movement on the workpieces they handle. For example, the above-noted conventional loader/unloader only imparts horizontal or rotational movement on the workpiece, but not at the same time. The gripping device only needs to grip the workpiece in such a way to avoid slipping from occurring during these specific movements. Accordingly, conventional loader/unloader units do not provide the secure grip needed when the parts are moved in a multi-directional path from one machine to another.
While robotics is well suited for some repetitious manufacturing operations, coordinating a robotic arm to go from machine to machine can be problematic. The robotic arms move quickly from one point to another, but have difficulty compensating when integrating tasks between different machines. For example, a machine that requires a degree of softness or compliance to load a workpiece onto a rotating tool or chuck is problematic for the rigid movements of the programmed robotic arm.
An additional problem associated with integrating a robot to work with several different machines is developing a practical end effector for such an activity. The speed and multi-directional movement of the robotic arm requires the end effector to be compact, balanced and light weight. An end effector that has excessive size or weight, or one that is unbalanced, will produce loads that will exceed the capacity of a given robotic arm. Accordingly, end effectors are typically designed to perform limited tasks and work with a specific machine. The robotic arm uses different end effectors to perform different tasks.
A further problem with both conventional robotic end effectors and conventional loader/unloaders is that they are not able to grip gear pieces having different sizes and shapes. The gripping mechanism on the loader/unloader has to be changed each time a different part run is made, which inhibits the ability to cost effectively produce smaller part runs.
The present invention is intended to solve these and other problems.
This invention relates to a multi-purpose end effector for a robotic arm that moves a workpiece through an automated, multi-station, manufacturing operation. The end effector is particularly useful in a gear manufacturing operation in which a gear piece is annealed, ground and tested to ensure it meets desired specifications. The relatively lightweight and compact end effector securely grips the workpiece during multi-directional movements, and provides a degree of softness when loading the normally non-rotating workpiece onto a continuously rotating chuck or tool. The end effector is secured to the robotic arm by a cross-member equipped with three different gripping implements. A central gripping device extends from the middle of the cross-member, a loading arm extends from one end of the cross-member, and an unloading arm extends from the other end. Each gripping implement includes pneumatically controlled gripping fingers for holding the gear pieces. Each loading and unloading arm has a gripping cylinder and a rotatable sleeve for supporting its gripping mechanism. The loading arm has an extension cylinder for extending its gripping mechanism with a degree of softness or resiliency that helps prevent binding when the normally non-rotating workpiece engages the rotating chuck or tool.
One advantage of the present end effector invention is its versatility. The end effector is equipped with several different gripping implements that permit its use with a variety of machines. One implement or gripping device is capable of performing operations that require the robotic arm to pick up or place a workpiece on a stationary tool or rack. This gripping device is capable of gripping the inside or outside surface of a workpiece or object. The other two gripping implements have a rotating sleeve that allows them to unload a workpiece off a rotating tool or chuck. One of these two implement is also equipped with an extension cylinder that gives the otherwise rigid movement of the robotic arm a degree of softness or compliance. This allows the gripping implement to smoothly load a non-uniformly shaped workpiece, such as a gear with teeth on its perimeter, onto the jaws of a rotating chuck without binding. The versatility of the end effector allows the robotic arm to move quickly from machine to machine without slowing down to change end effectors, which greatly improves the overall speed of the robotic arm and the entire manufacturing operation.
Another advantage of the present end effector invention is that it allows the robotic arm to simultaneously handle the movements, and loading and unloading of workpieces as they proceed from machine-to-machine or operation-to-operation in a multi-station manufacturing process. This is accomplished even though different operations may take longer than others. One operation may be to pick up a first gear, move it to and align it with a rotating chuck of a grinding machine, and smoothly load the gear on the rotating chuck. While the grinding operation is being performed, the end effector can pick up a second gear on a holding rack and move it to another rack for a relatively long annealing operation, and then pick up a third gear. After the grinding operation is performed, the end effector can unload the first gear from the rotating chuck, and load the third gear on the rotating chuck. While the grinding and annealing operations are being performed, the end effector can move and load the first gear in another machine at another station. In this way, the end effector can simultaneously handle several gears at different stages of the manufacturing process, which greatly increases the speed and efficiency of the robotic arm and the automated manufacturing process.
A further advantage of the present end effector invention is its compact, lightweight and balanced design. The straddled, in-line arrangement of the gripping and extension cylinders in the loading arm produces a compact and balanced design that is well suited for robotic applications. The generally symmetrical layout of the three gripping implements provides a further degree of balance that reduces the stresses on the robotic arm.
A still further advantage of the present end effector invention is that it enables a multi-station manufacturing operation to be performed in a relatively small, organized area, and reduces the cost of maintaining the machines and their down time. Expensive, bulky, machine specific loading/unloading units are eliminated, as are the supply and discharge conveyors and numerous holding bins. This reduces the amount of maintenance time for the manufacturing operation, as well as down time and potential injury to workers.
A still further advantage of the present end effector invention is that it reduces set up time and costs in an automated manufacturing operation, thereby enabling a smaller number of parts to be manufactured in a given part run such as in a just-in-time manufacturing operation. Each station in the operation does not need to be supplied with workpieces ready for that particular stage of processing. Instead, a small number of workpieces can be sent through the manufacturing operation by allowing the robotic arm and end effector to distribute the parts from station to station so that several workpieces are being simultaneously processed by different machines.
A still further advantage of the present end effector invention is that its gripping mechanisms are appropriate for a robotic application. The loading and unloading arms are each equipped with a pneumatic gripping cylinder that combines with a gripping mechanism with a mechanical lever to provide sufficient force to securely hold the workpiece as the robotic arm moves quickly through a variety of multi-directional movement patterns. This secure grip ensures the gear piece will remain in its desired gripped position on the end effector so that the robotic arm can accurately align the workpiece at the next station.
A further advantage of the present end effector invention is that it is able to grip and move a variety of gear pieces having different sizes and shapes. The gripping mechanisms on the end effector permit a wide range of motion of its gripping fingers. The same gripping mechanisms can be used in a variety of gear piece runs. This speeds up the time to change from one part run to another, and improves the machines ability to make the smaller part runs frequently found in a just-in-time manufacturing operation.
Other aspects and advantages of the invention will become apparent upon making reference to the specification, claims and drawings.